Eimer’s organ: touch receptors - 120 milliseconds to identify and consume prey 
The fastest predator on Earth: star-nosed mole
The Big Picture: Perception to Behavior
- Sensory processes begin with stimuli
- stimuli are forms of energy
- Receptors alert nervous systems
- use action potentials
- results in a ‘sensation’
- After a stimulus is processed, a motor response may be generated
Sensory Pathways
- Neurons =
- Most organelles inside cell body
- includes nucleus
- Highly branched extensions, called dendrites, receive signals
- Most neurons have a single axon to transmit signals
- transmit pulses of electrical current
- terminals connect cells
(1) Sensory Reception
- Sensory pathway starts with perception of sensations
- Sensory pathways have four basic functions:
- reception, transduction, transmission, perception
- (1) Sensory reception:
- sensory cells are specialized neurons
- inside or outside body
- detection of a stimulus
(2) Sensory Transduction: Converting signals
- Transduction:
- strength of stimulus determine how much
- Stimulus receptors change flow of ions across membranes
- opens/closes ion channels
- Ca2+, Na+, K+
- Membrane potential: gradient that forces ions to passively move in one direction
- can be processed by central nervous system
(3) Sensory Transmission: action potentials (nerve impulse)
- Transmission:
- Action potential:
- caused by change in membrane potential
- Receptor generates action potentials that travel to central nervous system
- large stimulus = more action potentials
Action Potential further explained…
(4) Sensory Perception: Processing the stimulus
- Perception:
- How does the brain know the difference in stimuli?
- action potentials are just electrical signals…
- Action potentials reach brain via dedicated neural pathways
- brain distinguishes stimuli on the path they arrive
If a tree falls in the woods……
Animal sensory receptors: Mechanoreceptors
- Response to touch, stretch, motion and sound
- Receptors sense physical deformation
- Ion channels linked to structures that end outside cell
- hair or cilia
- bending/stretching structure generates response
- Touch receptors often embedded in tissue
Diversity of mechanoreceptors on mouse face
Animal sensory receptors: Chemoreceptors
- (1) Transmit information about solute concentration
- detect change in blood solutes → stimulate thirst
- (2) Respond to individual kinds of molecules
- glucose, O2, CO2, amino acids
- Stimulus molecule binds to a chemoreceptor
- Chemoreceptor becomes more or less permeable to ions
- silk worms detect pheromones from females several kilometers away
Taste and smell rely on chemoreceptors
Taste and smell rely on chemoreceptors
Animal sensory receptors: Electromagnetic
- Receptors that detect light, electricity and magnetism
- Animals create & detect electromagnetic energy to hunt
- Used by animal kingdom to migrate
- proteins can sense Earth’s magnetic fields
- insects, birds & mammals
Animal sensory receptors: Electromagnetic
- Receptors that detect light, energy and magnetism
- may also create & detect electromagnetic energy
- Used widely by animals to sense prey
- 16% of fish species use electroreceptors to detect bioelectric fields from prey
Animal sensory receptors: Thermoreceptors
- Receptors detect heat and cold
- Hot pepper science has really helped!!!
- Receptors that respond to capsaicin also respond to high temperatures
- open a calcium channels
- taste ’hot": activate same receptors as hot soup
- opposite for ‘cold’ flavor
- Mammals: thermoreceptors for specific temperatures
- Venomous snakes: infrared receptors to detect ‘warm’ prey
Animal sensory receptors: Pain
- Pain receptors (nocioreceptors) detect stimuli that reflect harmful conditions
- damaged or inflammed tissues
- gene mutations can cause C.I.P.
- Respond to damaged/inflamed tissues
- perceived as pain
- trigger defenses (withdraw)
